This invention relates to a composite fabric for use as a clothing in the sheet forming zone of a papermaking machine.
Clothings of the aforementioned type are referred to as papermachine screens and are frequently comprised of two or three fabric layers which are complete in themselves and are interconnected by additional binder wires. In these types of clothings the lowermost fabric layer is made from relatively coarse threads or wires, since it is subject to considerable wear. The topmost fabric layer, on the other hand, since it supports the sheet of paper pulp, is made from fine wires so that it leaves no marks in the paper. While clothings structured in this manner were expected to result in negligible marking and to provide long service life and high stability, practical experience has not proven this out.
German patent applications (OS) Nos. 2,455,184, 2,455,185 and 2,917,694 disclose clothings comprised of a plurality of interconnected fabric layers. Each layer has interwoven longitudinal and transverse wires and the layers are exclusively interconnected by transverse binder wires. Unfortunately, clothings of this type have not reached their expected long service life, because the transverse wires are seriously degraded after a relatively short time of operation.
Canadian Pat. No. 711,428 and European patent application No. 0 044 053 disclose joining two fabric layers by interweaving the transverse wires of the lower fabric layer with the longitudinal wires of the upper fabric layer at regular intervals without the use of special transverse binder wires. However, with these composite fabrics, the risk of marking is very high.
It is, therefore, an object of the present invention to provide a composite fabric for use as a clothing in the sheet forming zone of a papermaking machine which causes but slight marking while having a long useful life.